Improving the PGU-450T Unit’s Maneuverability while Retaining Its Reliability and Economic Efficiency in Variable Load Modes

The article addresses the problem of securing reliable and economically efficient operation of cogeneration combined cycle power plants (CCPPs) taking the PGU-450 unit as an example during its operation at partial loads and performing control of the electrical loads in the condensing mode and heat and electrical loads in the cogeneration mode. The main constraints hindering wide-scale involvement of CCPPs to control of electrical and heat loads are noted. The need to switch the gas turbines, which feature limited capacities of bearing variable loads, into a mild operation mode with shifting the main load on the steam turbine is pointed out. A technology of PGU-450 operation at partial loads is suggested: CCPP unloading in accordance with the operation manual to the gas turbine permissible base load, e.g., according to the environmental constraint during its operation in the condensing mode, and further decrease of the power unit electric output at a constant base power output of the gas turbines and heat recovery steam generators through decreasing the steam turbine output by applying bypass steam admission or shifting a part of the high-pressure cylinder (HPC) or the entire HPS, or the steam turbine as a whole to operate in the generator-driven mode. The article presents the results of applying various bypass steam admission configurations during the CCPP operation in the condensing mode, including when shifting part of the HPC or the entire HPC, and the steam turbine as a whole is shifted to operate in the generator-driven mode when the CCPP is shut down in a standby mode in passing off-peak load hours. It has been shown that the use of bypass steam admission during the CCPP operation in the cogeneration mode is more economically efficient than it is in the condensing mode. The article also shows the advantage, in terms of reliability and economic efficiency, of shifting the steam turbine to operate in the generator-driven mode instead of its shutdown during the PGU-450 unit’s operation in the gas turbine unit‒combined heat and power plant (GTU‒CHPP) mode and passing the electric load curve off-peak hours.